Internal combustion engine comprising an exhaust gas recirculation system

ABSTRACT

An internal combustion engine includes a plurality of cylinders, an air intake line and an exhaust line collecting exhaust gas. The engine also includes an EGR line for rerouting a part of the exhaust gas from the exhaust line towards the air intake line and at least a first turbocharger comprising a first turbine driven by the exhaust gas flowing towards the atmosphere, linked to a first compressor located on the air intake line. The engine further includes a variable geometry EGR turbine located on the EGR line, driven by the EGR gas flowing in the EGR line. Thus, thanks to the pressure reduction occurring in the turbine, the EGR gas temperature is lowered, and less cooling power from the engine cooling system is required to cool down the EGR.

BACKGROUND AND SUMMARY

The present invention relates to an internal combustion enginecomprising an exhaust gas recirculation system, especially an internalcombustion engine dedicated to personal vehicles or industrialapplications, such as industrial vehicles or machines.

In many countries, environmental regulations impose an upper limit inengine NOx (nitrogen oxide and nitrogen dioxide) emissions, and infuture regulations, this limit will again be reduced.

One of the conventional ways of decreasing the level of NOx emissions ininternal combustion engines is to recirculate a portion of the exhaustgas back to the engine cylinders. This results in lowering thecombustion temperature and oxygen concentration and, as a consequence,limits NOx generation as NOx is generated by oxygen and hightemperature. Cooling the exhaust gas recirculation (EGR) gas beforereintroduction into the engine further reduces NOx emissions as thisallows the introduction into the cylinders of a greater mass of exhaustgas and increases mixture heat capacity.

To meet the current regulations, a typical internal combustion enginecan comprise as depicted on FIG. 1:

-   -   an air intake line 100 carrying intake air towards at least one        engine intake manifold 101 connected to each cylinder 102, said        air intake line 100 including an upstream low pressure        compressor 103 and a downstream high pressure compressor 104 as        well as an heat exchanger 105 (using the coolant of the engine        cooling system) located between the high pressure compressor and        the intake manifold 101;    -   an exhaust line 106 having at least one exhaust manifold 107        collecting the exhaust gas formed in each cylinder 102; said        exhaust line 106 can include two turbines 108, 109 driven by the        exhaust gas flowing from the exhaust manifold 107, each turbine        being mechanically connected to one of the compressors 103, 104;    -   an exhaust gas recirculation (EGR) line 110 whose inlet is        connected to the exhaust line 106 and whose outlet comes out in        an EGR mixer 111 connected to the air intake line 100, before        the intake manifold 101 and after the intake cooler 105, whereby        part of the exhaust gas is mixed with intake air and then        reintroduced into the engine cylinders 102.

A control valve 113 also referred to as EGR valve regulates the flow ofexhaust gas rerouted from the exhaust manifold 107 into the intakemanifold 101.

In such a known engine, the EGR gas is cooled before entering thecylinders 102 by means of an EGR cooler 112 located in the EGR line 110;this cooler 112 is usually an air/water heat exchanger using the coolantof the engine cooling system.

Consequently, the heat transferred from the hot exhaust gas to thecoolant can be significant, which can be detrimental to the coolingcapacity of the vehicle cooling system.

Tighter NOx emission regulations will therefore result in vehiclecooling systems needing more cooling power. Therefore, coolant pumpdesign could be problematic, and fuel consumption could be significantlyincreased as cooling fans may have to be engaged more often to meet theextra cooling need.

Another technical issue that has to be taken into account is the enginepressure differential. In order words, for the EGR gas to be able toflow from the exhaust manifold to the intake manifold, the enginepressure differential (which is the difference between exhaust pressureand intake pressure, i.e. dP=Pexhaust−Pintake) must be positive andsignificant enough. However, under specific engine operating conditions,exhaust backpressure can be lower than intake pressure (i.e. dP isnegative) or not high enough. This generally occurs at low engine speedsor low loads. Consequently, under these engine operating conditions, noor too little EGR gas is rerouted into the intake manifold, andtherefore NOx emissions cannot be reduced under the level imposed byregulations. This positive exhaust to intake pressure difference willalso affect engine efficiency and increase fuel consumption.

WO 01/14707 tackles the problem of EGR gas cooling and of engine coolingsystem overload. Under the teaching of this document, the EGR cooler hasto be oversized, as EGR gas flowing from this EGR cooler goes through acompressor and then is reintroduced into the intake manifold withoutfurther cooling.

Moreover, since a single turbine is provided on the exhaust line todrive two compressors, namely an intake air compressor and an EGR gascompressor, the engine thermodynamic efficiency is not optimized.

Another engine provided with an EGR system is described in WO 98/35153.According to this document, EGR gas flows through a radiator, and thenthrough a compressor before it is reintroduced into the intake manifold.Consequently, the EGR gas temperature increase taking place in the EGRcompressor can be compensated by a prior temperature reduction in theradiator, in which the EGR gas cooling is achieved by air flow.

While this arrangement is profitable since it does not entail anoverload of the engine cooling system, on the other hand it has severalother drawbacks.

In particular, in order to achieve a sufficient decrease in EGR gastemperature, the radiator must be large enough, and located in asufficiently open space to allow air to flow around it. However, avehicle has a complex structure which includes a large number ofcomponents (engine, cooling system, suspension system, transmissionsystem, hydraulic system etc.) which are very tightly arranged so as tominimize the overall size of the vehicle. The consequence is that thespace dedicated to accommodate the radiator can be severely limited.

More generally, the engine arrangement described in WO 98/35153 involvesmany conduits, and consequently many associated components such asvalves, etc. In addition to being complex, such a structure also lackscompactness.

JP-2001073884 discloses a turbocharged engine arrangement where theturbocharger is equipped with a waste gate to relieve the turbochargerwhen too much exhaust gases flow out of the engine. The waste gateejects excess gases in a line which is connected to the intake manifold,so that these gases are re-circulated. This line, which is branched-offthe waste-gate of the turbocharger, therefore forms a kind of EGR line,but it has the disadvantage that the EGR flow is directly linked to theamount of gas discharged from the waste-gate. Therefore, it is notpossible to control independently the flow of gases through the turbineof the turbocharger and the flow of EGR. Therefore, for certainoperating conditions, it is not possible to fully optimize the engine'soperation.

It therefore appears that there is room for improvement in the exhaustgas recirculation system in internal combustion engines.

It is an desirable to provide an improved internal combustion engineequipped with an exhaust gas recirculation system, which can overcomethe drawbacks encountered in current engines.

It is desirable to provide an engine where EGR gas can be cooled enoughwithout overloading the engine cooling system.

It is also desirable to provide an engine with a better thermodynamicefficiency.

Thus, the present invention provides, according to an aspect thereof, aninternal combustion engine that comprises a plurality of cylinders, anair intake line capable of carrying intake air towards an engine intakemanifold and an exhaust line capable of collecting exhaust gas from anexhaust manifold. The internal combustion engine also comprises an EGRline capable of rerouting a part of the exhaust gas from the exhaustline towards the air intake line and at least a first turbochargercomprising a first turbine driven by the exhaust gas flowing towards theatmosphere, mechanically linked to a first compressor located on the airintake line. The internal combustion engine further comprises a turbinelocated on the EGR line driven by the EGR gas flowing in the EGR line.The EGR turbine is of the variable geometry type.

With this arrangement, EGR gas flowing from the exhaust manifold goesthrough the EGR turbine prior to entering the EGR cooler. Due to thepressure reduction occurring in the turbine, the EGR gas temperature islowered, for example by as much as 100° C. Consequently, the EGR gastemperature at the EGR cooler inlet is lower than in the prior artengines. This makes it possible to reduce the load on the engine coolingsystem and to obtain a lower EGR gas temperature at the intake manifoldinlet, which means an even more reduced NOx level in the exhaust gas.Moreover, to achieve this goal, the invention does not require a largeand cumbersome radiator. It has to be noticed that, even if an air towater heat exchanger is still present in the engine to cool EGR gas, theheat rejection to the engine cooling system is however lowered thanks tothe invention, since the expansion through the EGR turbine makes itpossible to save a significant part of the vehicle cooling capacity. Thefact that the EGR turbine is of the variable geometry type allows anoptimal control of the EGR gas temperature and pressure reductionsthrough the EGR turbine. Indeed, the flow of EGR gas can thus beregulated by varying the geometry of the turbine. Indeed, a directeffect of varying the turbine geometry is to vary the pressure drop ofthe flow of EGR gases through the EGR turbine, which influences the flowof gases in the EGR circuit compared to flow of gas in the main exhaustline.

The EGR turbine being located on the EGR line is solely driven by EGRgas rerouted into the intake manifold, the EGR turbine is not driven byexhaust gas flowing towards the atmosphere. In other words, the EGRturbine is an EGR dedicated turbine, arranged in parallel with the firstturbine of the first turbocharger; all the flow passing through the EGRturbine is fed to the air intake line.

The EGR turbine being of the variable geometry type, no additional flowregulating valve needs to be provided in the EGR line upstream of theEGR turbine. This not only simplifies the construction and the controlof the engine arrangement, but it also allows to optimize both the flowof EGR and the EGR turbine operation in a combined way, achievingoptimum efficiency of the system.

According to a preferred implementation of the invention, the internalcombustion engine further comprises an energy recovering means linked tothe EGR turbine and capable of recovering the energy provided by the EGRturbine.

This important arrangement of the engine makes it possible to recoverthe energy produced by the EGR turbine in an appropriate energyrecovering means, which can directly use this energy or store it forfuture use. Consequently, thanks to this implementation of theinvention, on top of a better EGR temperature decrease, a better enginethermodynamic efficiency can be achieved.

Preferably, the EGR line outlet is connected to the air intake lineupstream from at least one compressor.

In that way, the invention makes it possible to manage engine airpressure differential dP, since the compressor forces EGR gas to flowtowards the intake manifold even at engine operating conditions when dPwould be opposite or favourable but too low. Therefore, the engine backpressure is significantly limited: EGR gas will naturally flow from ahigh pressure source to a low pressure source and fuel consumption canbe improved. Because there always exists an EGR gas recirculation,engine NOx emissions can be effectively reduced under the imposed level,whatever the engine operating conditions.

According to a first embodiment of the invention, the energy recoveringmeans is a second compressor mechanically connected to the EGR turbineand capable of compressing gas flowing from the first compressor outlettowards the intake manifold.

In this embodiment, the engine comprises two turbochargers whoseturbine, driven by exhaust gas or EGR gas, provides energy forcompressing intake air or a mix of intake air and EGR gas. The gasflowing in the air intake line towards the intake manifold can then passthrough a two-stage turbocharger. This arrangement may be implemented inorder to provide an intake pressure which is high enough to create afavourable engine pressure differential.

The second compressor can be located on the air intake line, downstreamfrom the first compressor. When needed, the air intake line may furthercomprise an additional compressor located downstream from the firstcompressor. This additional compressor is preferably situated betweenthe first and the second compressors, and may be part of an additionalturbocharger, the turbine of which being located on the exhaust lineupstream from the first turbine.

Alternatively, the second compressor is arranged in parallel with anadditional compressor located on the air intake line downstream from thefirst compressor.

According to a second embodiment of the invention, the energy recoveringmeans may be an energy storage component (such as a battery), acrankshaft mechanically or electrically connected to the EGR turbine, oran electrical device connected to the EGR turbine (such as an electricmotor or an alternator).

This second embodiment can be implemented when no compressor linked tothe EGR turbine is required on the air intake line to obtain asatisfactory engine pressure differential. Consequently, the energyprovided by the EGR turbine can either be directly used by anotherenergy recovering means, or stored in an energy recovering means for afuture use or for a use by another device located farther.

According to a third embodiment of the invention, the variable geometryEGR turbine is linked to a shaft of the at least first turbocharger saidshaft connecting the first turbine and the first compressor. In otherwords, this embodiment of the invention incorporates a single compressorwhich is driven by two turbines namely an EGR turbine driven by EGR gasand a turbocharger turbine driven by engine exhaust gas. In thisembodiment of the invention, the energy that is recovered on the EGRturbine is added to the energy that is recovered by the turbine of theengine turbocharger. The fact that at least the EGR turbine is of thevariable geometry type allows to operate both turbines at optimumoperating conditions, despite the fact that their rotation speed is notindependent while operating under possibly different and varying gasflows.

In order to increase the intake pressure, the air intake line mayfurther comprise an additional compressor located downstream from thefirst compressor. This additional compressor can be for example part ofan additional turbocharger the turbine of which is driven by exhaustgas.

The EGR line outlet can be connected to the air intake line upstreamfrom the only compressor or from the compressor located most upstream.This would result in a better mixing of EGR gas and intake air, and thusa better cooling of EGR gas since they may flow through more coolers andcompressors. Additionally, if several compressors are provided, EGR gaspressure would also be higher, which favours NOx emission reduction.

Alternatively, the EGR line outlet can be connected to the air intakeline downstream from the compressor located most upstream and upstreamfrom at least one other compressor. With this disposition, the EGR pipesmay be shorter, the engine being less expensive and more compact.

In an advantageous way, the exhaust manifold is arranged in two parts,each connected to a corresponding EGR pipe, the two EGR pipes meetingupstream from the first turbine. This prevents the EGR turbine fromgetting energy from only one part of the exhaust manifold, receivingonly a few exhaust pulses, which would lead to an irregular driving ofsaid turbine and to a poor efficiency.

Besides, the air intake line can further comprise at least one coolerlocated downstream from the EGR line outlet. This makes it possible tolower the EGR gas temperature in at least one cooler before it isreintroduced into the intake manifold.

For example, the air intake line can include:

-   -   an intake cooler located downstream from the compressor situated        most downstream, and upstream from the intake manifold;    -   and/or at least one intake cooler located between two        compressors when at least two compressors are present.

These and other advantages will become apparent upon reading thefollowing description in view of the drawing attached heretorepresenting, as non-limiting examples, embodiments of an engineaccording to the invention.

DESCRIPTION OF FIGURES

The following detailed description of several embodiments of theinvention is better understood when read in conjunction with theappended drawing being understood, however, that the invention is notlimited to the specific embodiments disclosed. In the drawing,

FIG. 1 is a schematic drawing of an internal combustion engine of theprior art;

FIGS. 2-5 are schematic drawings of an internal combustion engineaccording to several variants of a first embodiment of the invention.

FIGS. 6 and 7 are schematic drawings of an internal combustion engineaccording to several variants of a second embodiment of the invention.

FIG. 8 is a schematic drawing of an internal combustion engine accordingto a third embodiment of the invention.

DETAILED DESCRIPTION

An internal combustion engine 1 typically comprises an engine block 2defining a plurality of cylinders 3, namely six cylinders in theembodiments illustrated in the figures. The number and arrangement ofcylinders as illustrated in the drawings is of course purely indicative.

Intake air is carried towards an intake manifold 4 feeding the cylinders3, through an air intake line 5. The gas formed in each cylinder 3 canbe collected by an exhaust manifold 6 arranged in two halves. An exhaustline 7 connected to the exhaust manifold 6 carries one part of the gas(exhaust gas) towards the atmosphere. The other part of the gas (EGRgas) is carried by two circuits 8, 9, each connected to one half of theexhaust manifold 6. These circuits 8, 9 meet and form a single EGR line12 whose outlet comes out in an EGR mixer 13 connected to the air intakeline 5. In the shown embodiments, the EGR line is also provided with anEGR cooler 14 using the engine coolant, located downstream of themeeting point of conduits 8, 9.

The engine 1 can further include at least a first turbocharger. Thefirst turbocharger can be a low pressure turbocharger having a turbine15 located on the exhaust line 7, and a compressor 16 located on the airintake line 5. The engine 1 further comprises a second turbine which isa dedicated EGR turbine 17 located on the EGR line 12, downstream fromthe meeting point of conduits 8, 9 and upstream from the EGR cooler 14.

In the following, it is understood that the EGR turbine 17 is of thevariable geometry type. Various types of variable geometry turbines areavailable on the market, usually incorporated in stand-aloneturbocompressors.

As an examplen Honeywell Turbo Technologies offers Multivane™ VariableGeometry Turbochargers which employ a mobile system composed of a numberof vanes that pivot on their axis to modify the cross section on theinlet of the turbine housing. An electronically controlled rotaryelectric actuator helps to channel gas to the turbine wheel, enablingprecise control of boost pressure over a vast load and speed range. TheVNT™ Slidevane™ Turbochargers models, also from Honeywell TurboTechnologies, employ a mobile nozzle piston system to modify the crosssection. Cummins Turbo Technologies offers Holset VGT™ turbochargers inwhich the vanes do not pivot but slide axially. In the case of the VTGturbocharger from BorgWarner Turbo Systems, variable geometry isachieved using guide vanes located in front of the turbine wheel.

Thanks to the use of a variable geometry EGR turbine, it is possible todispense with the usual EGR valve, or any other valve in the EGR line 7upstream of the turbine, while still achieving optimal control of theflow of EGR gases, thus ensuring perfect match to the engine's instantoperating parameters through the variation of the turbine geometry. Atthe same time, EGR turbine working conditions are also optimized.

Several embodiments of the invention will now be described; the sameelements in each embodiment bear the same reference numerals.

In a first embodiment of the invention, illustrated in FIGS. 2 5, thevariable geometry EGR turbine 17 is part of a high pressureturbocharger, the compressor 18 of which is located on the air intakeline 5 downstream from the low pressure compressor 16.

The air intake line 5 can be provided with a first intake cooler 19located between low pressure compressor 16 and high pressure compressor18, and with a second intake cooler 20 located downstream from the highpressure compressor 18 and upstream from the intake manifold 4. Bothcoolers 19, 20 can suitably use an engine coolant from the enginecooling system.

As depicted in FIGS. 2 and 3, the engine 1 is equipped with a two-stageturbocharger and, thus, a high boost pressure can be achieved.

In the embodiment described in connection with FIG. 2, the EGR mixer 13is located upstream from low pressure compressor 16; intake air mixedwith EGR gas flow through two coolers 19 and 20 and two compressors 16and 18; this has the advantage of a better mixing between intake air andEGR gas, a better cooling of EGR gas and a higher gas pressure at theintake manifold 4. Another significant advantage is that it is possibleto get high EGR rates even if boost pressure, i.e. intake pressure, ishigher that exhaust pressure.

In the embodiment described in connection with FIG. 3, the EGR mixer 13is located downstream from low pressure compressor 16 and upstream fromfirst intake cooler 19. With this arrangement, the EGR circuit isshorter, and then more compact. And since EGR gas still flows throughone compressor and two coolers, efficient mixing and cooling can beobtained, as well as a high enough intake pressure; it should also benoted that this embodiment has the further advantage of a good balanceof the low pressure turbocharger as almost the same mass flow goesthrough the low pressure compressor 15 and through the low pressureturbine 16.

In the variant described in connection with FIG. 4, the engine 1 isequipped with a three-stage turbocharger, since an additionalturbocharger is provided. This additional turbocharger comprises aturbine 21 located on the exhaust line 7 upstream from the turbine 15 ofthe low pressure turbocharger and a compressor 22 located on the airintake line 5 downstream from first intake cooler 19 and upstream fromhigh pressure compressor 18. An additional cooler 23 can also beprovided on the air intake line 5 between intermediate compressor 22 andhigh pressure compressor 18. In other words, the implementation of FIG.4 corresponds to a conventional two-stage turbocharger architecture(with two turbines on the exhaust line and two compressors on the airintake line) with a third compressor linked to the EGR turbine, in orderto increase the final boost pressure. The three compressors areconnected in series.

In the variant of FIG. 5, there is also provided an additionalturbocharger, comprising a turbine 24 located on the exhaust line 7upstream from the turbine 15 of the low pressure turbocharger and acompressor 25 located on the air intake line 5, downstream of the lowpressure compressor 16 and of the first intake cooler 19 and upstreamfrom second intake cooler 20. However, the compressor 18 driven by theEGR variable geometry turbine is located on a parallel line 26 whoseinlet is connected to the air intake line 5 upstream from high pressurecompressor 25 and whose outlet is connected to air intake line 5,through a valve 27, downstream from intermediate compressor 25. A singledirection flow valve 27 has to be used to prevent gas from the highpressure compressor 25 from flowing towards the compressor 18 outlet,which could generate surge. Compressors 25 and 18 are here set inparallel.

It has to be noticed that FIG. 5 shows no pipe meeting in EGR line 12,but an EGR line 12 whose inlet is connected to the exhaust manifold 6.However an arrangement with two conduits, as in FIG. 4, can be envisaged(not shown). A further arrangement could be to introduce the EGR mixerupstream of the low pressure compressor (not shown).

A further embodiment of the invention is shown in FIGS. 6 and 7.

In this embodiment, EGR turbine 17 is not linked to a compressor locatedon the air intake line, but to another type of energy recovering means30 which is capable of recovering the energy provided by the turbine.Depending on the vehicle needs, this energy recovering means 30 maycomprise:

-   -   an energy storage component (such as a battery);    -   and/or a crankshaft mechanically or electrically connected to        turbine 17;    -   and/or an electrical device connected to turbine 17 (such as an        electric motor or an alternator);    -   and/or any other component capable of directly using the energy        provided by turbine 17 or storing this energy for a future user        for a use by another device. This embodiment can be very        attractive as vehicle electric energy needs tend to grow to        power more vehicle electrical equipments such as air        conditioning, GPS system etc. For example, the component could        provide electricity to an engine accessory such as the oil pump        or the water pump, which would help to distribute coolant to EGR        cooler, etc.

The mechanical connection may be achieved by means of a viscous couplingor other appropriate coupling.

In the arrangement of FIG. 6, a single turbocharger is provided suitablycomprising turbine 15 and compressor 16. The air intake line 5 isequipped with only one cooler (first intake cooler 19), and the EGRmixer 13 is situated upstream from the compressor 16. However, otherimplementations can be envisaged.

FIG. 7 shows an alternative arrangement where the engine 1 is providedwith a two-stage turbocharger:

-   -   a low pressure turbocharger comprising turbine 15 and compressor        16;    -   a high pressure turbocharger comprising an additional turbine 31        located on exhaust line 7 upstream from turbine 15 and a high        pressure compressor 32 located downstream from low pressure        compressor 16, a first intake cooler 19 being situated between        the two compressors 16, 32.

In this arrangement, the EGR mixer 13 may be situated upstream from lowpressure compressor 16. However, other implementations can be envisaged(more coolers, different location for EGR mixer, etc.).

It is possible to envisage that the energy recovering means 30 couldparticipate in controlling the EGR rate, in addition to the presence ofthe variable geometry turbine, if an electric machine is used, byaccelerating or decelerating the EGR dedicated turbine.

FIG. 8 illustrates a further embodiment of the invention whereby the EGRturbine 17 can be directly linked to the shaft of the standardturbocharger. In other words the compressor 16 can be driven by theturbine 15 and by the EGR turbine 17. This embodiment of the inventionincorporates a single compressor 16 and two separate turbines 15 and 17;the engine includes two turbine inlet ports: one turbine inlet port,corresponding to the first turbine 15 is dedicated to the standardexhaust system, and the other turbine inlet port, corresponding to theEGR turbine 17, is dedicated to the EGR circuit. In this embodiment ofthe invention, EGR gas that have been cooled by flowing through the EGRturbine 17, can be further cooled by an EGR cooler 14 before joining theair intake line 5 upstream from the compressor 16. By connecting on thesame shaft both the turbine 15 driven by the engine exhaust gas and theEGR turbine 17 driven by EGR gas, an extra driving power is provided tothe compressor 16. Overall this embodiment of the invention is lessdemanding on the vehicle cooling system while making an optimized use ofthe energy contained in the exhaust gas and in the EGR gas. It can alsobe envisaged that this latter embodiment of the invention which isprovided with a twin-turbine turbocharger could integrate a two stageturbocharged arrangement where said twin-turbine turbocharger would beused in cooperation with a low pressure turbocharger in an arrangementsimilar the one depicted on FIG. 4.

In this embodiment, it is particularly useful to have a variablegeometry EGR turbine. Indeed, in this embodiment, the rotating speeds ofthe two turbines are directly linked. They are equal, or could be simplylinked by a multiplying factor if one of the turbines would be linked tothe common shaft through a gear train. Therefore, there being nopossible independent adjustment of the speed of the turbine, it is verybeneficial to be able to adapt the geometry of the EGR turbine 17 tomatch turbine speed and EGR flow in order to have the best possibleefficiency of the turbine, which translates both in an optimum coolingof the EGR gases and a maximum energy recovery on the compressor side.

Of course, the invention is not restricted to the embodiments describedabove by way of non-limiting examples, but on the contrary itencompasses all embodiments thereof. Particularly, while, in the aboveembodiments, the nature of the turbines 15, 21 24 located in the exhaustline 7 has not been discussed, it is of course always possible to choosefrom a regular turbine or a variable geometry turbine similar to the EGRturbine 17, knowing that regular turbines usually have a better maximumefficiency ratio. Also, the EGR lines 8, 9, 12 can be connected eitherdirectly to the exhaust manifold, as shown in FIGS. 2 to 8, or connectedto an upstream part of the exhaust line 7, as shown in the prior art atFIG. 1. Moreover, in the shown embodiments of the invention, the EGRline 12 has its inlet connected to the exhaust line upstream of anyturbine located on said exhaust line. This feature allows having maximumpressure of the EGR gas, and therefore having the maximum flow of EGRgases whatever the engine operating conditions. Nevertheless, especiallyin the case of applications requiring less EGR gases, it is possible tohave the EGR line inlet branched-off downstream of at least one turbinelocated in the exhaust line. For example, with an arrangement similar tothat of FIG. 7, it would be possible to have the EGR line branched-offbetween turbines 31 and 15. In an arrangement similar to that of FIG. 4,the same disposition could be applied, although it might require havingthe corresponding EGR driven compressor 18 located more upstream in theintake line 5, at least upstream of compressor 22, and possibly upstreamalso of compressor 16.

Also, with the EGR line comprising a turbine, it might be useful toprovide means to prevent fouling of the turbine by particles containedin the exhaust fumes coming out of the cylinders. Therefore, it can beprovided that such means may be inserted in the EGR line upstream of theEGR turbine, or even in the exhaust line, upstream of the branch-offlocations of the EGR line. Such means can comprise a diesel particulatefilter operated with periodical recycling, or a catalytic regenerativetrap where the particles are burnt through a catalytic process. Thelatter means may be used thanks to the upstream location, near theexhaust manifold, where the gas temperatures are high enough for thecatalytic process.

In the above, it has been described embodiments where the EGR lineoutlet is connected to the air intake line upstream from at least onecompressor. Such a configuration is preferred because the pressuredifferential makes it possible for EGR gases to flow towards the intakemanifold at any engine operating condition, at also allows to take out amaximum of the energy contained in the EGR gases before reintroducingthem into the air intake circuit. Nevertheless, the invention can alsobe implemented with a so-called “short-route” EGR circuit where the EGRline outlet is connected to the air intake line downstream of thecompressor(s). Such a configuration has the advantage of not having therisk of fouling the compressors with residues carried by the EGR gases.

1. An internal combustion engine having a plurality of cylinders,comprising: an air intake line capable of carrying intake air towardsthe cylinders; an exhaust line capable of collecting exhaust gas fromthe cylinders; an EGR line capable of rerouting a part of the exhaustgas from the exhaust line towards the air intake line; at least a firstturbocharger comprising a first turbine driven by the exhaust gasflowing towards the atmosphere, mechanically linked to a firstcompressor located on the air intake line; an EGR turbine located on theEGR line, the EGR turbine being solely driven by the EGR gas flowing inthe EGR line; and an energy recovering means linked to the EGR turbineand capable of recovering the energy provided by the EGR turbine,wherein the energy recovering means is a second compressor mechanicallyconnected to the EGR turbine and capable of compressing gas flowing fromthe first compressor outlet towards the cylinders; wherein the EGRturbine is of the variable geometry type, and the flow of EGR gas isregulated by varying the geometry of the turbine, an inlet of the EGRline is upstream of any turbine located on the exhaust line, and anoutlet of the EGR line is connected to the air intake line upstream fromat least one compressor in the air intake line.
 2. The internalcombustion engine according to claim 1, wherein no additional flowregulating valve is provided in the EGR line upstream of the EGRturbine.
 3. The internal combustion engine according to claim 1, whereinthe second compressor is located on the air intake line, downstream fromthe first compressor.
 4. The internal combustion engine according toclaim 1, wherein the air intake line further comprises an additionalcompressor located downstream from the first compressor.
 5. The internalcombustion engine according to claim 4, wherein the second compressor isarranged in parallel with the additional compressor located on the airintake line downstream from the first compressor.
 6. The internalcombustion engine according to claim 1, wherein the EGR line outlet isconnected to the air intake line upstream from the first compressorlocated most upstream of any other compressor in the air intake line. 7.The internal combustion engine according to claim 1, wherein the airintake line further comprises an additional compressor locateddownstream from the EGR line outlet.
 8. The internal combustion engineaccording to claim 1, wherein the EGR line comprises an EGR coolerdownstream of EGR turbine.
 9. An internal combustion engine having aplurality of cylinders, comprising: an air intake line capable ofcarrying intake air towards the cylinders; an exhaust line capable ofcollecting exhaust gas from the cylinders; an EGR line capable ofrerouting a part of the exhaust gas from the exhaust line towards theair intake line; at least a first turbocharger comprising a firstturbine driven by the exhaust gas flowing towards the atmosphere,mechanically linked to a first compressor located on the air intakeline; an EGR turbine located on the EGR line, the EGR turbine beingsolely driven by the EGR gas flowing in the EGR line; wherein the EGRturbine is of the variable geometry type, and the flow of EGR gas isregulated by varying, the geometry of the turbine, an inlet of the EGRline is upstream of any turbine located on the exhaust line, and anoutlet of the EGR line is connected to the air intake line upstream fromat least one compressor in the air intake line, wherein the EGR lineoutlet is connected to the air intake line downstream from the firstcompressor located most upstream of any other compressor in the airintake line and upstream from at least one other compressor.
 10. Theinternal combustion engine according to claim 9, wherein no additionalflow regulating valve is provided in the EGR line upstream of the EGRturbine.
 11. The internal combustion engine according to claim 9,wherein the at least one other compressor linked to the EGR turbine andcapable of recovering the energy provided by the EGR turbine, whereinthe at least one other compressor mechanically connected to the EGRturbine and capable of compressing gas flowing from the first compressoroutlet towards the cylinders.
 12. An internal combustion engine having aplurality of cylinders, comprising: an air intake line capable ofcarrying intake air towards the cylinders; an exhaust line capable ofcollecting exhaust gas from the cylinders: an EGR line capable ofrerouting a part of the exhaust gas from the exhaust line towards theair intake line; at least a first turbocharger comprising a firstturbine driven by the exhaust gas flowing towards the atmosphere,mechanically linked to a first compressor located on the air intakeline; an EGR turbine located on the EGR line, the EGR turbine beingsolely driven by the EGR gas flowing in the EGR line; wherein the EGRturbine is of the variable geometry type, and the flow of EGR gas isregulated by varying the geometry of the turbine, an inlet of the EGRline is upstream of any turbine located on the exhaust line, and anoutlet of the EGR line is connected to the air intake line upstream fromat least one compressor in the air intake line, wherein the exhaustmanifold is arranged in two parts, each connected to a corresponding EGRconduit, the two EGR conduits meeting upstream of the EGR turbine. 13.The internal combustion engine according to claim 12, wherein noadditional flow regulating valve is provided in the EGR line upstream ofthe EGR turbine.
 14. The internal combustion engine according to claim12, further comprising an energy recovering means linked to the EGRturbine and capable of recovering the energy provided by the EGR turbinewherein the energy recovering means is a second compressor mechanicallyconnected to the EGR turbine and capable of compressing gas flowing fromthe first compressor outlet towards the cylinders.